1. Field of the Invention
The invention concerns sunscreen composite particles for use in cosmetic compositions to deliver protection against ultraviolet radiation.
2. The Related Art
Ultraviolet radiation can be damaging to skin. Immediate damage may be in the form of erythema. More long term is the concern of initiating cancerous growth. For these reasons, photoprotective agents known as sunscreens have been incorporated into cosmetic products.
Organic sunscreen agents have a number of disadvantages. Under the influence of ultraviolet radiation, the sunscreen agents themselves are known to degrade. Photostability may only be a matter of hours. Consumers thinking that they are fully protected with their sunscreen application, often expose themselves for a time beyond the photostability limit. Further, organic sunscreen agents can under certain circumstances cause skin irritation. A still further problem is that some sunscreen agents may not be fully compatible with other sunscreen or formulation components.
Attempts have been made to address the aforementioned problems. One approach has been to encapsulate the sunscreen agent. A few encapsulates are commercially available.
A first commercial material is known as Sun Caps 664® sold by Particle Sciences, Inc. of Bethlehem, Pa. Sun Caps 664® is formulated with a concentration of octylmethoxycinnamate (OMC) of 21.5% encapsulated in a binder that includes beeswax, carnauba wax, Vinyl Pyrrolidone/Eicosene Copolymer and emulsifiers (PEG-100 stearate, PEG-20, bis-PEG-12 dimethicone, sorbitan tristearate and Steareth-100). Sun Caps® are formed in a process revealed in U.S. Pat. No. 5,733,531. The encapsulates are supplied as an aqueous dispersion containing up to 65% solids.
Another hydrophilic composite particulate commercially available is sold by Rona Division of EMD Chemicals under the trademark Eusolex® UV Pearls® OMC. UV Pearls® OMC is prepared and described in U.S. Pat. No. 7,264,795. This material is delivered as 40% particles in 60% aqueous carrier. The particles are structured with a core of greater than 70% octylmethoxycinnamate surrounded by a coating of about 10% silica, about 1-2% polyvinylpyrrolidone (as binder), and minor ingredients.
While the known encapsulates have shown some advantages, much improvement remains to be done with respect to enhanced activity and photostability. The present invention has sought to address these issues.